EOR 101 – A primer into enhanced oil recovery

In her second post, Terrex Energy Inc.'s Kim Davies writes about how to wring new oil out of old plays

By Kim Davies

August 15, 2011

We are living in exciting times, or perhaps scary times, depending on your point of view. But no matter what happens in the political and financial worlds there will be a need for oil for a long time. But this remaining oil is more difficult to access and produce economically.

Terrex Energy is meeting this challenge by focusing on enhanced oil recovery (EOR); the process of getting more oil out of existing mature pools. We know how much oil was there, how much has been produced and how much is left. A significant benefit to EOR projects is in the use of existing wells and pipelines to minimize environmental impact and keep costs down. But the right EOR technology needs to be applied to allow significantly more oil to be released from the reservoir.

So what are these technologies? To be clear, because of physical processes within the earth, a significant amount of oil is immovable, no matter how big a pump jack you employ or how much water you inject to push the oil to the producer wells. As a basic concept, EOR techniques all work by “scrubbing” the oil from the reservoir rock by using processes to either alter the viscosity of the oil or the water in the reservoir. I often liken the use of regular oilfield production practices to EOR to having grease on your hands and the comparison between washing them with water or washing them with soap. The soap is much more effective at cleaning your hands.

The major EOR methods use thermal, gas or chemical processes and what follows are very simple descriptions of each. Thermal processes involve heating the oil to reduce its viscosity and allow it to flow more easily. Steam injection is a typical thermal approach, the most widely used in the world, and very common in Canada.

There are a number of gas processes, all of which are injected into the reservoir to enhance reservoir pressure and act as solvents (soaps). The most common gases used are carbon dioxide, hydrocarbon and nitrogen. A little used gas is actually plain air. It’s used for in situ combustion and has seen some significant successes. Chemical EOR’s use is rapidly expanding and offers great potential. The chemicals employed can be made up of polymers (a thickening agent), which reduce excess water production and allows more oil to be forced to producer wells. In addition, the chemicals employed can be a combination of polymer, alkaline and surfactant (ASP). In this case, the chemicals act as solvents to reduce the interfacial tension between oil and injected water permitting significantly more oil to be freed for production.

There is no one-size-fits-all approach to an EOR design. Each reservoir has characteristics that need to be carefully considered to determine the appropriate EOR method. Terrex’s approach is to study oil pools where EOR has been applied successfully and target those types of pools and processes in our acquisition and development plans. It’s also important to look at the cases where EOR has not been that successful; these can be just as informative. Terrex’s initial focus, mainly as a result of opportunity, is on the use of chemical water floods for medium to light oil pools.